Eye care products, such as contact lens care systems, are susceptible to contamination by ocular pathogens. Known ocular pathogens include bacteria, fungi, and also protozoans such as amoebae, for example the acanthamoebae. Acanthamoebae are ubiquitous free-living protozoans, which exist in two distinct morphological forms: the trophozoite and the cyst. The trophozoite form is the free swimming form and is relatively easy to kill. The organism encysts in an adverse environment, creating a thick protective coat making it very difficult, to kill. The cyst form is the hibernating form of the organism. The organism reverts to the trophozoite form in a favorable environment.
A variety of species of Acantharnoeba have been found to cause infectious keratitis. These species include A. polyphaga, A. castellanii, A. lenticulata, A. hatchetti, A. astronyxis, A. culbertsoni, A. rhysodes, and others. See, for example, Ma et al., Rev. Infectious Diseases 1990 May/June; 12(3):490-513 and the references cited therein. Moreover, acanthamoebae use bacteria and fungi as a food source. Co-contamination of contact lens care system with bacteria and fungi facilitates the growth of the acanthamoebae in the contact lens care system, and is thus implicated as a risk factor for acanthamoebic keratitis.
The incidence of ulcerative keratitis among soft contact lens wearers in the United States has been found to be a function of contact lens wear mode. An incidence of infection of 4.1 per 10,000 daily wear patients per year and 20.9 per 10,000 extended wear patients per year has been found. Thus of the approximately 20 million contact lens wearers in the United States, over 12,000 infections (from all causes) occur yearly. Acanthamoebic keratitis has been reported in contact lens wearers regardless of lens type.
Various agents have been found to be effective in killing and/or inhibiting the growth of bacteria or fungi. For example, U.S. Pat. No. 4,499,077 to Stockel discloses an antimicrobial composition for soft contact lenses including an oxidizing agent such as an oxyhalogen compound, e.g., stabilized chlorine dioxide or hydrogen peroxide, and a polymeric germicide, e.g., a quaternary ammonium polymer or an amino and/or imino polymer or salts thereof. U.S. Pat. No. 4,654,208 to Stockel discloses an antimicrobial composition for contact lenses including an aqueous solution of a germicidal polymeric nitrogen compound and an oxidizing agent, e.g., chlorine dioxide, chlorite, stabilized chlorine dioxide or hydrogen peroxide, to potentiate the activity of the germicidal polymeric nitrogen compound at low concentrations. However, no agents have been proposed as effective in inhibiting the growth of protozoans.
It would be desirable to inhibit the growth of protozoans such as acanthamoebae in eye care products such as contact lens solutions, in order to reduce the incidence of acanthamoebic keratitis and other ophthalmic pathologies due to the presence of protozoans.